Discovery of small-molecule natural products that target cellular bioenergetics

Molecular-targeted antitumor therapy has found favor in antitumor drug discovery programs. Hypoxia (\u3c 5% oxygen) is a comfeature of solid tumors and hypoxia-inducible factor-1 (HIF-1) represents an important antitumor target. Bioenergetic homeostasis is typically altered in tumor cells and HIF-1 plays an important role to produce a glycolytic phenotype. Glycolysis inhibitors are an emerging class of potential tumor-selective adjuvant therapeutic agents. Natural product aerobic glycolysis inhibitors may enhance the effectiveness of current therapies. Mitochondrial oxidative phosphorylation inhibitors in botanical dietary supplements (BDS) possess a potential health hazard which should be identified and appropriately regulated. Chapter one briefly reviews the molecular-targeted natural product antitumor drug discovery process. Descriptions of tumor hypoxia, HIF-1, HIF-1 regulatory pathways and the effect of HIF-1 on tumor cell bioenergetics are presented. Cellular bioenergetic pathways and natural products that inhibit HIF-1 by interfering with cellular bioenergetics are discussed. Mitochondriotoxic small-molecule natural products reported previously are further reviewed. Chapter two discusses the effect of chromatographic media on molecular-targeted antitumor drug discovery. A panel of crude extracts was eluted through columns of various chromatographic media using a step gradient method. Total recoveries from the various columns and various elution protocols were compared and statistically analyzed. The crude extracts and column eluates were evaluated for HIF-1 inhibitory activity. Chapter three discusses the development of a bioenergetics-based screening method to screen crude extracts for glycolysis inhibitors. Crude extracts (10,648) were screened and seven hits (hit rate 0.72%) were identified. Bioassay-guided isolation of Moronobea coccinea crude extract resulted in isolation of a protonophoric compound moronone (1) (false positive). The structure of 1 was determined by a combination of spectroscopic and spectrometric means. The protonophoric compounds must be rapidly dereplicated for successful discovery of glycolysis inhibitors. Chapter four discusses the screening of BDS products and pure compounds for mitochondrial uncouplers or electron transport chain inhibitors. The blue cohosh (Caulophyllum thalictroides) extract and three saponins cauloside A (3), saponin PE (4) and cauloside C (5) permeabilize the mitochondrial membrane. Sesamin (6) and guggulsterol III (7) and guggul (Commiphora wightii) extract inhibit mitochondrial complex I. These extracts and compounds are cytotoxic in nature